Method for bonding heat sinks to overmolds and device formed thereby

Abstract

A method for bonding heat sinks to packaged electronic components comprises the steps of: (a) exposing to a plasma a surface of a molded polymer formed on a substrate; (b) allowing the plasma to at least partially convert silicon-containing residue on the surface to silica; and (c) bonding an article to the surface by applying an adherent between the article and the surface. Often, the silicon-containing residue is silicone oil, a mold release compound, which may prevent the formation of a bond when using conventional bonding methods and materials. The silica layer formed on the surface of the molded polymer assists in formation of a proper bond. The plasma may be an oxygen plasma and the adherent may be selected from either a heat cured silicone-based paste adhesive with a metal oxide filler or a heat cured porous polymer film impregnated with adhesive. In particular, the film may be polytetrafluoroethylene, the adhesive may be polybutadine, and the film may be further impregnated with a metal oxide heat transfer medium, such as zinc oxide. An alternate method comprises applying the porous polymer film without plasma treatment and heat curing the film to form a proper bond.

We claim:  
     
       1. An apparatus, comprising: 
       a molded polymer formed on a substrate, wherein the molded polymer comprises an overmold;  
       silicon-containing residue on a surface of the overmold;  
       an adherent material bonded to the surface of the overmold; and  
       an article bonded to the adherent material, wherein the article comprises a heat sink, and wherein a bond strength between the heat sink and the surface of the overmold is greater than a bond strength between the overmold and the substrate.  
     
     
       2. The apparatus of  claim 1 , wherein the substrate comprises an electronic component. 
     
     
       3. The apparatus of  claim 1 , wherein the adherent material comprises a porous polymer film impregnated with epoxy adhesive. 
     
     
       4. The apparatus of  claim 3 , wherein silicon-containing residue comprises silicone oil, the film comprises polytetrafluoroethylene, the adhesive comprises polybutadine, and the film is further impregnated with a metal oxide heat transfer medium. 
     
     
       5. The apparatus of  claim 4 , wherein the metal oxide heat transfer medium comprises zinc oxide. 
     
     
       6. The apparatus of  claim 1 , wherein the heat sink comprises anodized. 
     
     
       7. The apparatus of  claim 1 , wherein the heat sink comprises chromated aluminum. 
     
     
       8. The apparatus of  claim 6 , wherein a bond formed between the heat sink and the overmold comprises a lap sheer strength between about 300 psi to about 800 psi.